1. Field of the Invention
The present invention relates to a process and apparatus for moulding and curing tyres for vehicle wheels.
2. Description of the Related Art
In the production cycle of a tyre, following a tyre forming process in which the various components of the tyre are made and/or assembled, a moulding and curing process is carried out for the purpose of defining the structure of the tyre according to a desired geometry, normally including a specific tread pattern.
For this purpose, the green tyre (in the present text, this term denotes a tyre which has not yet been moulded and cured) is enclosed in a mould cavity which is formed inside a curing mould and which is shaped according to the geometric configuration of the outer surfaces of the tyre to be produced.
When the curing is complete, the mould is opened for the removal of the tyre.
A tyre generally comprises a carcass structure, in the shape of a toroidal ring, including one or more carcass plies, reinforced with reinforcing cords lying in radial planes (in the case of what are known as radial tyres), in other words in planes containing the axis of rotation of the tyre. The ends of each carcass ply are fixed to at least one metal annular structure, usually known as the bead core, which reinforces the beads, in other words the radially inner extremities of said tyre, which serve to fit the tyre on a corresponding mounting rim. A strip of elastomeric material, called the tread band, is placed on the crown of said carcass structure, and a relief pattern for ground contact is formed in this tread band at the end of the curing and moulding steps. A reinforcing structure, usually known as the belt structure, is placed between the carcass structure and the tread band. In the case of a car, this belt structure usually comprises at least two radially superimposed strips of rubberized fabric provided with reinforcing cords, usually metallic, positioned parallel to each other in each strip and crossing the cords of the adjacent strip, the cords being preferably positioned symmetrically about the equatorial plane of the tyre. Preferably, said belt structure also comprises a third layer of fabric or metal cords placed circumferentially (at 0 degrees), in a radially outer position, at least on the ends of the underlying strips.
Sidewalls of elastomeric material are also applied to the corresponding lateral surfaces of the carcass structure, each extending from one of the lateral edges of the tread band to the position of the corresponding annular structure for fixing to the beads.
The term “elementary components” in the present description and in the subsequent claims denotes elementary finished intermediate products in the form of a continuous elongate element of elastomeric material, which may comprise at least one textile or metal reinforcing cord, which may be cut to size.
Among the known procedures for forming tyres having the structure described above, some procedures have recently been developed in which the green tyres are produced from a limited number of elementary components supplied to a forming support. This procedure of forming from elementary components is an alternative to the conventional method of forming from finished intermediate products, which requires the separate production and storage of the various tyre components, such as the carcass plies, the bead cores, the belt strips, the tread band, and the sidewalls, to mention only a few, and it is preferable to the conventional method when tyres are to be produced in small batches or in specific sectors, for example, and/or in applications such as building high-performance or competition tyres. In the latter cases, this preference is based, in particular, on the greater uniformity, due to the lack of joints between the finished intermediate products.
For example, WO 00/35666 in the name of the present applicant describes a method and apparatus for forming a tyre by making its components directly on a toroidal support, in which some components are produced by feeding a continuous elongate element by means of an extruder, the element being conveniently distributed on the toroidal support while the support is rotated about its own axis.
U.S. patent application No. US 2003/0141627, published in the name of the Goodyear Tire & Rubber Company, describes a method and apparatus for moulding tyres with a radially extendable moulding ring for the beads. When extended, the bead moulding ring has a radial circumferential surface facing outwards for moulding the beads. The bead moulding rings each comprise a plurality of segments, half of which are first segments which are complementary to second segments and alternate circumferentially with the latter.
European patent application EP 0368546 relates to a method and apparatus for bladderless tyre moulding. A bladderless tyre moulding press comprises two platens, namely an upper and a lower platen, and means for moving the platens relative to each other from an open position to a closed moulding position, platen mounting means for moulding the sidewalls of the tyre, and means for moulding the tread band. Each of the platen mounting means serves to mould a corresponding bead of the tyre, and the bead moulding means include central means which are movable with respect to the corresponding platens for insertion into the tyre. Each platen includes bead moulding means which, when extended, form a surface for moulding an inner surface of the beads. The platens retain the beads and seal them against the sidewall plate of the mould, thus enabling a pressurized fluid to be introduced into the tyre.